Countersink holes are commonly used throughout industry where it is necessary or desirable to recess the head of a fastener, such as a screw or rivet. For example, countersink holes are extensively employed in the aircraft industry, where rivets are used to attach an outer skin to frame members. In this application, it is particularly important that the top of the rivet be flush with the outer surface of the skin, otherwise non-flush rivets disturb the air flow over the skin, creating turbulence which adds drag to the aircraft. Consequently, it is important that the tapered side walls of the hole countersink have a precise depth calculated so that the top of the rivet is precisely flush with the skin surface.
A number of gauge devices exist for measuring features of countersinks, such as depth and diameter, however these prior devices sometimes yield erroneous measurements due to the fact that a probe forming part of the gauge is not precisely centered within the countersink hole opening. This misalignment problem stems from the fact that gauges are normally used in combination with fixtures that are used to drill the countersink hole. Such fixtures typically an opening provided with a bushing for supporting and guiding a drill motor and countersink bit. After the countersink hole is formed, the gauge is inserted through the guide bushing which theoretically is precisely aligned with the central axis of the countersink hole. However, due to bushing wear, tolerance stack-up of tool features and other factors, the central axis of the gauge is not, in fact, always precisely aligned with the central axis of the countersink hole. This axial offset causes the probe to contact only a portion of the tapered side wall in the countersink, thereby preventing it from being fully seated around the entire circumference of the tapered side wall, in turn generating error in the measurement.
Accordingly, there is a need in the art for a countersink gauge having a self-centering probe which overcomes the deficiencies of the prior art discussed above. The present invention is directed towards satisfying this need.